Machine tool with an automatic tool exchanger

ABSTRACT

A machine tool is provided with an exchange arm for automatically exchanging tools between a tool spindle and a tool magazine. A drive key and a detent pin protrude respectively from the tool spindle and each of the tool storage portions of the magazine and are engageable, with a predetermined play, with a key-way of each tool. A fine indexing device has a rotatable cam drum on which a first cam segment is formed for indexing the tool spindle to a predetermined angular position following a coarse indexing operation by a coarse indexing device. A second cam segment is further formed on the cam drum to rotate the tool spindle more than the play from said predetermined angular position after a fresh tool is inserted into the spindle, so that a positive engagement between the drive key and the key-way of the tool can be achieved.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to machine tools and, moreparticlarly, to a machine tool with an automatic tool exchanger forexchanging a tool received in a tool spindle with another tool selectedout of a tool magazine.

2. Description of the Prior Art

In a known machine tool of this kind, a drive key and a key-waycomplemental thereto are provided respectively on a tool spindle andeach of the tools to transmit the driving force of the tool spindle tothe tool received therein, and the tool spindle is arranged to beindexed to a predetermined angular position prior to a tool exchangeoperation. At tool holding portions of a tool magazine, there areprovided detent members with which the key-ways of the tools arerespectively snugly engaged, so as to prevent the tools from angularlymoving even a little in the stored state. Furthrmore, the drive key andthe key-way are machined to almost the same width, such as, for example,the former being 25.4 mm. wide, the latter being 25.7 mm. wide, andthus, when engaged, to establish little clearance or play therebetweenso as not to permit relative rotation between the tool spindle and thetool received by the same.

In the prior art machine tool, therefore, when the tool is presentedonto the tool spindle, with its key-way not being exactly aligned withthe drive key, the performance of an automatic tool exchange operationbecomes impossible since, in such an event, the drive key necessarilyinterferes with a flange portion of the tool. This trouble occurs,though rarely, due to the fact that there appear many technicaldifficulties in exactly holding all of the tools stored within the toolmagazine at the same angular position and also in presenting the tool tothe tool spindle with its key-way being exactly aligned with the drivekey.

SUMMARY OF THE INVENTION

Accordingly, it is a primary object of the present invention to providea machine tool with a tool exchanger having high reliability inoperation.

Another object of the present invention is to provide a machine toolwith an improved tool exchanger in which a drive key of a tool spindleand a key-way of each tool are determined to facilitate a tool insertioninto the tool spindle, as well as into a tool magazine, and neverthelessthe drive key positively drives the tool when the tool spindle isrotated.

A further object of the invention is to provide a machine tool with animproved tool changer, as above, which uses a peculiar cam mechanism forindexing a tool spindle to a predetermined angular position and foreffecting a positive contact between a drive key and a key-way of eachtool.

Briefly, the foregoing and other objects are achieved, according to thepresent invention, through the provision of an improved machine toolwhich comprises a rotatable tool spindle for receiving a tool, a toolmagazine for removably storing a plurality of tools, an exchange arm forexchanging tools between the tool spindle and the tool magazine, acoarse indexing device for stopping the tool spindle within apredetermined angular extent after a machining operation, and a fineindexing device composed of a movable cam member provided with a camsegment for indexing, to a predetermined angular position, the toolspindle having been indexed within the angular extent.

The tool spindle is provided at one end thereof with a drive key, withwhich a key-way, formed upon each tool, is engageable with apredetermined play. At tool storage portions of the magazine, there arerespectively provided a plurality of detents in the same angularrelationship with one another, each of which has almost the same widthas that of the drive key.

The movable cam member is further provided with another cam segment forrotating the tool spindle a little from the predetermined angularposition after a fresh tool is inserted by the exchange arm into thetool spindle. Accordingly, a relative rotation is made between the toolspindle and the inserted fresh tool, so that the drive key can bebrought into a positive drive relation with the key-way of the freshtool.

BRIEF DESCRIPTION OF THE DRAWINGS

Various other objects, features, and attendant advantages of the presentinvention will be more fully appreciated as the same becomes betterunderstood from the following detailed description when considered inconnection with the accompanying drawings, in which like referencenumerals designate like or corresponding parts throughout the severalviews, and wherein:

FIG. 1 is a schematic diagram illustrative of the basic tool exchangeoperation of the present invention;

FIG. 2 is a front elevation view of a machine tool constructed inaccordance with the present invention;

FIG. 3 is a longitudinal sectional view of the apparatus taken along theline III--III of FIG. 2;

FIG. 4 is a fragmental longitudinal sectional view of the apparatustaken along the line IV--IV of FIG. 3;

FIG. 5 shows an expansion plan of the cam drum shown in FIG. 4;

FIG. 6 is a longitudinal sectional view of the apparatus taken along theline VI--VI of FIG. 2, showing particularly one of the storage socketsmounted upon the tool magazine;

FIG. 7 is a longitudinal sectional view of the apparatus taken along theline VII-VII of FIG. 6;

FIG. 8 is a partial ladder diagram of an electric control circuitemployed within the apparatus of the present invention;

FIG. 9 shows a modification of the fine indexing device shown in FIG. 4;and

FIG. 10 shows an expansion plan of the cam drum shown in FIG. 9.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings and more particularly to FIG. 1 thereof,illustrative of the basic tool exchange operation of the invention,there is provided a tool spindle 10, from one end of which a drive key10a protrudes to be engageable, with play, with a key-way 11a cut out ona flange of a tool or a tool holder 11. In the state indicated by thesolid line, clearances, each corresponding to an angle α, areestablished between the drive key 10a and both side walls of the key-way11a, and the tool spindle 10 and the tool 11 are thus relativelyrotatable within an angular extent 2d.

Generally, the tool or the tool holder 11 which is extensively used inthis field has a tapered shank of National Taper (N.T.) No. 50, and thekey-way 11a of the tool 11 is machined to be 25.7 mm wide. In thepresent invention, the width of the drive key 10a is made narrower,within the range of 5 to 70%, than that of the key-way 11a. In thisinstance, the clearance between the drive key 10a and the key-way 11aincreases by an angle of 0.9° each time the width of the drive key 10ais reduced 1mm. However, it should be noted that if the width of thedrive key 10a is made narrower, within a range less than 5% of that ofthe key-way 11a, the advantage resulting from such is scarcely obtained,and that if the width of the drive key 10a is made narrower, by morethan 70% relative to that of the key-way 11a, a problem may occur withinthe strength of the drive key 10a.

the tool 11 stored in a tool holding portion, which is in a tool removalstation of a tool magazine 24, is removed therefrom and presented ontothe tool spindle 10 by a tool exchange arm 13 which operates, in order,through an extension movement, a rotational movement of an angle of180°, and a withdrawal movement. A detent pin 14 protrudes at the toolholding portion of the tool magazine 24 and is engaged with the key-way11a of the tool 11 with a play of an angular extent 2α, within which thetool 11 is therefore rotatable. Although, in FIG. 1, only one toolholding portion is shown, which has been indexed to the tool removalstation, it is apparent that a detent pin 14 is provided at each of thetool holding portions in the same angular relationship with one another,that is, at the three o'clock position of each tool holding portion, asshown in FIG. 1. As the exchange arm 13 is such that it is rotatedthrough an angle of 180°, the tool spindle 10, prior to a tool transferoperation, is so stopped as to position the drive key 10a at apredetermined angular position corresponding to the detent pin 14 in thetool removal station, namely at the nine o'clock position, as shown inFIG. 1, and in this condition, the tool transfer operation is performed.

Thus, even when the key-way 11a of the tool presented by the toolexchange arm 13 onto the tool spindle 10 is deviated within an angularextent of ±α from the nine o'clock position, it is possible for thekey-way 11a of the tool 11 to be engaged with the drive key 10a, owingto the provision of the clearance 2α. Accordingly, the problem of thetool exchange operation being interrupted because of the interferencebetween the drive key 10a and the key-way 11a is avoided, wherebyreliability in the exchange operation is enhanced. In the machine toolaccording to this invention, the clearance α, which appears between rearsurfaces of the drive key 10a and the key-way 11a, is eliminated beforea machining operation by rotating the tool spindle 10 and, therefore,there can also be realized a tool drive superior to those of knownapparatus with respect to its reliability.

Referring to FIGS. 2 to 7, a preferred embodiment will now be described.A machine tool illustrated in FIG. 2 has a column 20, on which a spindlehead 21, rotatably supporting a tool spindle 10, is guided to beslidable in a vertical direction. On a work table 22, which is slidablein longitudinal and transverse directions relative to the column 20,there is indexably mounted a rotary table 23, onto which a workpiece Wis attachable. A tool magazine 24 for storing a plurality of diversetools 11 is indexably mounted on the top of the column 20. Between thetool magazine 24 and the tool spindle 10, there is provided an automatictool exchanger 15, having an exchange arm 13, which is provided with apair of grippers 13a, 13b at both ends thereof. Tools 11, 11 storedwithin the tool magazine 24 and received in the tool spindle 10 aregripped by the grippers 13a, 13b, removed therefrom, mutually replacedthrough the rotation of an angle of 180°, and inserted thereinto and, insuch a manner, a tool exchange operation is carried out.

As best shown in FIG. 3, the tool spindle 10 is formed at one endthereof with a tapered bore 12 for receiving the tool 11 and is providedwith a drive key 10a protruding from the end face. The tool 11, wheninserted into the tapered bore 12, is firmly clamped upon the toolspindle 10 as a pull stud 16, protruding from its rear end, is drawn bya snap member 32, connected with one end of a drawing rod 31, which aset of washer springs 30 are always drawing in a rearward direction. Inface to face relation with the rear end of the drawing rod 31, there isdisposed an unclamping cylinder 33, a piston 34 of which, when advanced,compresses the washer springs 30, so as to advance the drawing rod 31and to thereby release the pull stud 16 from the snap member 32, so thatremoval of the tool 11 becomes possible.

A gear member 35 is keyed on the tool spindle 10 substantiallyintermediate the length of the same. On the gear member 35, there areformed, in spaced relation, a large gear 35a and a small gear 35b, withboth of which a shiftable gear member 36 is selectively engageable. Theshiftable gear member 36 is held upon and spline-engaged with a splineshaft 38, which is in turn connected with an output shaft 37a of anelectrical motor 37. A coupling 39 is provided with a disc 39a, to whicha brake unit 40 is disposed to press its brake pads. A dog 42 is securedupon the forward end of the tool spindle 10 at a predetermined angulardisposition. When electrical conduction to the motor 37 is stopped aftera machining operation, but rotation of the tool spindle 10 stillcontinues because of its inertia, an appropriate switch PRS1 securedupon the spindle head 21 is activated by the dog 42, to energize thebrake unit 40, so that the tool spindle 10 can be stopped within apredetermined angular extent (coarse index).

At the rear end of the tool spindle 10, there is secured an index plate41 having a protrusion 41a. After being positioned by the brake unit 40,the dog 42 and the approximate switch PRS1, within such a predeterminedangular extent 2α, as to be engageable with a pair of index claws 43a,43b, as shown in FIG. 4, the protrusion 41a of the index plate 41 getssandwiched between the index claws 43a, 43b, which then approach eachother, and is thus indexed to a predetermined angular position. Namely,the above constitutes a fine indexing device generally indicated by thereference numeral 48, the detail of which will be described hereinbelow.A pair of pilot bars 44, only one being shown, are fixed on the spindlehead 21 to be extended tangentially of the index plate 41, and the indexclaws 43a, 43b are mounted on and slidable along the pilot bars 44.Follower pins 49a, 49b, embedded in the rear ends of the index claws43a, 43b, are engaged, respectively, at spherical head portions thereofwith two closed cam slots 45a, 45b formed on the circumferential surfaceof a cam drum 45, which is supported on the spindle head 21 to berotated about its axis parallel with the bars 44. The cam drum 45 isdrivingly connected at its one end with an index motor 46 mounted on thespindle head 21 so as to be rotated thereby in one direction, the motor46 containing a speed reduction mechanism.

As shown expanded in FIG. 5, at an angular position θ1, the cam slots45a, 45b are respectively formed parallel along the upper and lowerverges of the cam drum 45 and, thus, the index claws 43a, 43b, guidedthereby, are respectively withdrawn from the rotational locus of theprotrusion 41a to the most open condition, as indicated by the phantomline in FIG. 4, so as to permit the rotation of the tool spindle 10.When a limit switch LS1 is activated by a dog 47a, it is detected thatthe index claws 43a, 43b are at the angular position θ1 of the cam drum45. A first cam segment CS1 extends from the angular position θ1 toanother angular position θ2', within the extent of which the cam slots45a, 45b gradually approach each other to sandwich the protrusion 41abetween the index claws 43a, 43b, whereby the protrusion 41a, havingbeen positioned within the angular range or extent 2β, is indexed to thethree o'clock position, as shown in FIG. 4. Another limit switch LS2 isprovided to detect another angular position θ2 of the cam drum 45, whenactivated by a dog 47b. Furthermore, a second cam segment CS2 is definedbetween the position θ2' and another angular position θ3, within theextent of which the cam slots 45a, 45b are inclined upwardly with aparallel relation to each other. Accordingly, within this extent, theindex claws 43a, 43b are upwardly moved together with the protrusion 41asandwiched thereby, which thus rotates the index plate 41 and thespindle 10 a little in a counterclockwise direction, as viewed in FIG.4. A third cam segment CS3 extends from the position θ3 to the positionθ1, between which the cam slots 45a, 45b are gradually separated fromeach other so as to remove the index claws 43a, 43b from the rotationallocus of the protrusion 41a.

An exchange arm 13, as shown in FIG. 6, is fixed on one end of a hollowshaft 50 which is able to both rotate about its own axis and move in astraight axial line. Within a support housing 51 for operably supportingthe hollow shaft 50, there are formed cylinders 54 and 56, the former ofwhich slidably contains therein a piston rack 53 movable perpendicularlyof the hollow shaft 50, and the latter of which slidably contains apiston 55 movable parallel to the hollow shaft 50. The piston rack 53 ismeshed at its rack tooth portion 53a with a spur gear 50a cut upon theouter periphery of the hollow shaft 50 and is allowed to move in itsaxial direction in such meshed condition, thus causing rotation of thehollow shaft 50. A piston rod 57 of the piston 55 is connected with ahydraulic distributor 58, which, at the rear end of the hollow shaft 50,is so arranged as to be rotatable relatively thereto, that is, to permitrotation of the hollow shaft 50 therewithin, but to move integrallytherewith in the axial direction, and thus, the reciprocation movementof the piston 55 can cause the hollow shaft 50 to move forwardly andrearwardly therewith.

At both the ends of the exchange arm 13, a pair of grippers 13a, 13b areprovided being pivotably supported about pivot pins 60, 61, on whichpinions 62, 63 are keyed, which are in turn meshed through idle pinions64, 65 with rack bars 66, 67 slidable radially of the hollow shaft 50,respectively, as best shown in FIG. 7. The inner ends of the rack bars66, 67 are pivotably connected, respectively, to one end of links 68,69, of which the other ends are mutually overlapped and pivotablyconnected with one end of a floating link 70. The other end of thefloating link 70 is pivotably connected to a slider 71 inserted into thehollow shaft 50, and the slider 71 is further connected through a rod 74to a piston 73 inserted into a gripping cylinder 72 which is formed atthe rear end of the hollow shaft 50, within the hydraulic distributor58. Therefore, when the piston 73 is forwardly moved, pushing thefloating link 70 to radially extend the links 68, 69, the rack bars 66,67 are moved away from each other, so that each pair of grippers 13a,13b are closed to grip the tools 11. To the contrary, the rearwardmovement of the piston 73 causes the links 68, 69 to be folded, movingthe rack bars 66, 67 toward each other and consequently, the grippers13a, 13b are opened to release the tools 11.

From each of the tool holding portions of the tool magazine 24, as shownin FIGS. 2 and 7, there protrudes, at the three-o'clock position, adetent pin 14, by which the key-way 11a of the stored tool 11 isprevented from deviating from the three o'clock position more than theangular extent ±α. The aforementioned drive key 10a has substantiallythe same width as those of the detent pins 14 in its rotationaldirection.

The operation of the apparatus constructed as above will now bedescribed. When a machining operation is completed, the spindle head 21is moved upwardly to be positioned at the uppermost travelling end, asshown in FIG. 2, and at the same time, the rotation of the tool spindle10 is stopped in the following manner. That is, as the motor 37 is firstde-energized and then, the brake unit 40 is energized at the time whenthe approximate switch PRS1 detects that the tool spindle 10 reaches apredetermined angular position, the tool spindle 10 is stopped to placethe protrusion 41a of the index plate 41 within the predeterminedangular extent, as shown in FIG. 4 (coarse index). Upon the completionof the coarse indexing operation, the index motor 46 is energized untilthe cam drum 45 is angularly moved from the position θ1 to the positionθ2, whereby the index claws 43a, 43b are moved toward each other to beclosed. Accordingly, the protrusion 41a is angularly adjusted andpositioned at the nine o'clock position accurately corresponding to thedetent pin 14 (fine index).

The tool magazine 24 has beforehand been rotationally indexed to presenta fresh tool 11, to be next used, to the tool removal station or toolexchange station. As soon as the fine indexing operation is completed,the grippers 13a, 13b of the exchange arm 13 are closed tosimultaneously grip a previously used tool 11, received within the toolspindle 10, and the fresh tool 11 indexed to the exchange station. Theunclamping cylinder 33 provided at the rear end of the tool spindle 10,is operated to advance the piston 34, pushing the drawing rod 31 againstthe washer springs 30, so that the used tool 11 is unclamped. Followingthis, the exchange arm 13 is advanced by the forward movement of thepiston 55, and accordingly of the hollow shaft 50, to remove the tools11 from the tool spindle 10 and the tool holding portion, andsubsequently, the piston rack 53 is operated to rotate the hollow shaft50 and the exchange arm 13 therewith through an angle of 180°.Accordingly, the tool 11 removed from the spindle 10 is aligned with thetool holding portion, and the tool 11 from the same with the spindle 10.

The rearward movement of the piston 55 is then effected to rearwardlymove the hollow shaft 50 and to retract the exchange arm 13 therewithand, as a result, the used tool 11 and the fresh tool 11 are insertedrespectively into the tool holding portion and the tool spindle 10. Inthis tool insertion, since the key-way 11a of the fresh tool 11 is heldwithin the angular extent ±α with the nine o'clock position as thecentral figure, the tools 11, 11 are inserted respectively withoutinterfering with the drive key 10a of the tool spindle 10 and the detentpin 14 of the tool holding portion. In this event, between the drive key10a and the key-way 11a of the fresh tool 11, there appears a clearancewhich reaches 2α at its maximum, but nevertheless positive drive of thetool 11 by the drive key 10a is achieved in the following manner.

That is, when the tool insertion operation is completed, the index motor46 is energized to rotate the cam drum 45 from the angular position θ2to θ1 and thus, both the index claws 43a, 43b are upwardly moved by anamount Δl, as indicated in FIG. 5, on the way up to the angular positionθ3. Accordingly, the index plate 41, along with the tool spindle 10, isrotated a little in the counterclockwise direction, so that no clearanceis formed between the drive key 10a and one of the key-way wallsdrivingly urged thereby.

The piston 34 of the unclamping cylinder 33 is thereafter moved in therearward direction to clamp the fresh tool 11 upon the tool spindle 10by means of the force of the washer springs 30, and then, the grippers13a, 13b are opened to release the tools 11, 11. The spindle head 21 isimmediately moved toward the machining position and, at the same time,the spindle drive motor 37 is operated to rotate the tool spindle 10 inthe counterclockwise direction. Accordingly, another machining operationis initiated in such a condition that the fresh tool 11 is positivelyand certainly driven by the drive key 10a.

FIG. 8 shows a portion of an electric control circuit employed toaccomplish the above-described operation. When a normally open contactcr100 is closed, upon the completion of the coarse indexing operation, amagnetic relay CR110 is energized and self-held, since a normally opencontact crM06 for instructing the tool exchange operation has alreadybeen closed. The energization of the relay CR110 operates the indexmotor 46 to rotate the cam drum 45. When a normally open contact ls2 ofthe limit switch LS2 is closed, a magnetic relay CR111 is energized andde-energizes the relay CR110 by opening its normally closed contactcr111x. The cam drum 45 is angularly moved from the position θ1 to theposition θ2, so that the tool spindle 10 is indexed to the predeterminedangular position.

The relay CR111, when energized, causes a well-known tool exchangecontrol circuit TECC to operate the exchange arm 13 because its normallyopen contact cr111 is provided therein as a start instruction.Therefore, the exchange arm 13, as previously mentioned, simultaneouslygrips the fresh and used tools 11, 11, removes the tools 11, 11 from thetool magazine 24 and the tool spindle 10 after the tool unclampingoperation is carried out with the tool spindle 10, rotates through anangle of 180°, and inserts the tools 11, 11 respectively, into the toolmagazine 24 and the tool spindle 10. Upon the completion of the toolinsertion operation, the tools are still being gripped by the grippers13a, 13b, whose gripping force is, however, temporarily weakened, and inthis connection, a magnetic relay CR135 is then energized throughnormally open contacts cr111, cr112 and cr128 and a normally closedcontact cr136x. The energization of the relay CR135 operates the indexmotor 46 again so as to further rotate the cam drum 45, whereby positiveengagement is brought about between the drive key 10a and the key-way11a of the fresh tool 11.

When a normally open contact ls1 of the limit switch LS1 is closed, amagnetic relay CR136 is energized to de-energize a magnetic relay CR113and the relay CR135 by opening its normally closed contacts cr136x.Thus, the fresh tool 11 is clamped upon the tool spindle 11, and theindex motor 46 is de-energized so as to cause the index claws 43a, 43bto remain opened and thereby to allow the rotation of the tool spindle10. When the tool clamping operation is completed, a limit switch LS5 isactivated, a normally open contact ls5 of which is therefore closed, toenergize a magnetic relay CR137. A normally closed contact cr137x of therelay 137 is thus opened to de-energize the relay CR112, whereby thetools 11, 11 are released from the exchange arm 13. As the completion ofthe tool release operation results in closing a limit switch contactls6, a magnetic relay CRFM06 is energized to de-energize the relaysCR111 and CR136 by opening its normally closed contacts crFM06x andcrFM06x. The energization of the relay CRFM06 is regarded as a completeinstruction of the auxiliary function M06, so that, as mentioned above,another machining operation is initiated from this stage.

FIG. 9 shows another stop mechanism modified from that shown in FIG. 4.In this modification, a cam drum 45, disposed with its axis extendingtangentially of the tool spindle 10, is provided with a cam way, alongwhich the index protrusion 41a is directly guided. As shown expanded inFIG. 10, the cam way is defined by one cam slot 45c, which effects uponthe index protrusion 41a the same indexing movement as the cam slots45a, 45b, shown in FIG. 4, do through the index claws 43a, 43b.Accordingly, it is noticed that the dimension of the cam slot 45cexactly corresponds to that of a land portion 45c' defined, as shown inFIG. 4, by the cam slots 45a, 45b.

Obviously, other modifications and variations of the present inventionare possible in light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims, the inventionmay be practiced otherwise than as specifically described herein.

What is claimed as new and desired to be secured by Letters Patent ofthe United States is:
 1. In a machine tool with an automatic toolexchanger having a tool spindle rotatably supported and capable ofreceiving a tool at one end thereof, a tool magazine for removablystoring a plurality of tools, and exchange means for exchanging toolsbetween said tool spindle and said tool magazine, the improvementcomprising:a drive key protruding from said one end of said tool spindleand engageable, with a predetermined play in its rotational direction,with a key-way formed on each of said tools; a plurality of detentsprovided on said tool magazine in the same angular relationship with oneanother and respectively engageable with said key-ways of said tools,each of said detents having almost the same width as that of said drivekey in the rotational direction of each tool; coarse indexing means forindexing said tool spindle within a predetermined angular extent after amachining operation; and fine indexing means comprising means providedon said tool spindle for integral rotation therewith, a movable cammember operably supported and being drivingly connectable with saidmeans on said tool spindle when the same is indexed within saidpredetermined angular extent, said cam member being provided with afirst cam segment cooperating with said means on said tool spindle forindexing said tool spindle to a predetermined angular position when afirst movement of said cam member is effected and a second cam segmentcooperating with said means on said tool spindle for rotating said toolspindle a little from said predetermined angular position when a secondmovement of said cam member is effected, and cam drive means connectedto said cam member for generating said first movement of said cam memberafter said tool spindle is indexed within said angular extent by saidcoarse indexing means and for generating said second movement of saidcam member after a fresh tool is inserted into said tool spindle by saidexchange means.
 2. A machine tool as set forth in claim 1, wherein saidcam member is a cam drum disposed to be rotatable about an axisextending tangentially of said tool spindle, and wherein said cam drivemeans comprises a drive motor for rotating said cam drum selectivelythrough said first and second movements.
 3. A machine tool as set forthin claim 2, wherein said first and second cam segments are formed uponthe circumferential surface of said cam drum and communicated with eachother.
 4. A machine tool as set forth in claim 3, wherein said secondcam segment is defined to rotate said tool spindle from saidpredetermined angular position more than said predetermined playestablished between said drive key and said key-way of said fresh tool.5. A machine tool as set forth in claim 4, wherein said means on saidtool spindle is an index protrusion protruding radially of said toolspindle, said cam drum being drivingly connectable to said indexprotrusion so as to adjust the angular position thereof in accordancewith said first and second cam segments.
 6. A machine tool as set forthin claim 5, wherein said first cam segment is formed to graduallyrestrain the rotatable angular extent of said index protrusion, so asthereby to index said tool spindle to said predetermined angularposition, and wherein said second cam segment is extended helically ofsaid cam drum.
 7. A machine tool as set forth in claim 6, wherein saidcam drum is further provided with a third cam segment communicating fromsaid second cam segment to said first cam segment and formed togradually release said index protrusion from the restraint by said camdrum.
 8. A machine tool as set forth in claim 4, wherein said cam drumis provided with two closed cam slots on each of which said first andsecond cam segments are defined, and wherein said fine indexing meansfurther comprises:guide means extended in parallel relation with theaxis of said cam drum, and a pair of indexing claws slidably guided onsaid guide means and respectively engaged with said closed cam slots soas to be selectively opened and closed, said indexing claws beingconnectable with said means on said tool spindle to index said toolspindle to said predetermined angular position when closed and permitthe rotation of said tool spindle when opened, and said means on saidtool spindle being an index protrusion protruding radially of said toolspindle.
 9. A machine tool as set forth in claim 8, wherein said firstcam segments defined on both of said cam slots gradually approach eachother as the angular position of the cam drum advances, so as to movesaid indexing claws from an open condition to a closed condition, andwherein said second cam segments defined on both of said cam slots areextended herically of said cam drum with a parallel relation, so as toallow said indexing claws to integrally move along said guide means assaid indexing claws remain in said closed condition.
 10. A machine toolas set forth in claim 9, wherein said cam slots respectively definethereon third cam segments communicating from said second cam segmentsto said first cam segments and gradually separating from each other soas to release said index protrusion from the restrain by said indexingclaws.
 11. A machine tool as set forth in claim 9, wherein said fineindexing means further comprises control means for controlling theoperation of said drive motor, said control means comprising:first andsecond detectors for respectively detecting said open and closedconditions of said indexing claws, a first control circuit forenergizing said drive motor when said second detector is activated,after said tool spindle has been indexed within said angular extent bysaid coarse indexing means, and a second control circuit for energizingsaid drive motor when said first detector is activated, after said freshtool has been inserted into said tool spindle by said exchange means.